Cutting sections of piezo crystals



C. B. SAWYER CUTTING SECTIONS OF PIEZO CRYSTALS Filed Jan. 26, 1928INVENTOR ATTORNEY June 17, I930.

Patented June 17, 1930 UNITED STATES PATENT OFFICE CHARLES B. SAWYER, OFCLEVELAND HEIGHTS, OHIO, ASSIGN-OR, BY MESNE ASSIGN- MENTS, TO THECLEVELAND TRUST COMPANY, OF CLEVELAND, OHIO, A CORPORA- TION OI OHIOCUTTING SECTIONS OF IP IEZO CRYSTALS Application filed January 26, 1928.Serial No. 249,778.

This invention relates to piezo-electrio crystals of the Rochelle salttype and more particularly to an improved method of cutting sectionsfrom such crystals.

| It is frequently necessary in using crystals of the Rochelle salt typeto cut them into portions of various shape to procure the desiredsections for accomplishing various results in their application toacoustic apparatus. It has been customary to do this cutting with a wetstring which is usually made to run over pulleys and is applied withwater. The cutting action seems to be the result of a combination ofabrasion and solution and at best is somewhat tedious and not ada ted torapid production of sections of the esired shape and orientation fromRochelle salt crystals.

The thickness of the sections to be cut from the Rochelle salt crystalsis usually quite a small dimension in comparison with one or both of theother dimensions of the section, that is, the width and length, andconsequently it has been relatively difficult to out such sections withsubstantially uniform thickness in an eflicient manner from the frailand brittle Rochelle salt crystals.

In addition to the extreme brittleness of crystals of the Rochelle salttype, these crys- 80 tals have a low melting point, a e coefficient ofthermal expansion and low heat -conductivity, and these severalproperties make it very diflicult to readily cut sections from such acrystal. It has been found, however, that by carefully givingconsideration to these various properties Rochelle salt crystals can besawed successfully and efliciently under certain conditions as disclosedin my process.

In order to successfully saw such sections from a brittle crystal of theRochelle salt type it is necessary to prevent the application of even' asmall side pressure to the sides of the crystal when a kerf is being cutthrough a crystal. It is also necessary in view of the large coeflicientof thermal expansion and the low heat conductivity of the crystal toavoid, as far as possible, frictional effects on the crystal, such asrubbing 50 or abrasion on the sides of the kerf, as these wouldnecessarily raise the temperature of a localized portion of the crystaland thus cause cracking or breaking of the crystal. Furthermore, owingto the low melting point of the crystal, frictional or abrasive actionby the saw tends to melt a minute portion of the crystal dust whichthereby becomes attached to the saw. Such dust may be melted directly onthe saw blade or may become firmly attached to the sides of the sawblade by being pressed against the saw blade while the blade istraveling through the saw guides. Any such adhesion' of packed or moltencrystalline dust to the blade increases the effective Width of the sawand also fills up the interstices between the teeth, thereby furtherincreasing the frictional eifect. It will be seen that the frictionaleffects are therefore cumulative. As a Rochelle salt crystal begins tomelt at approximately degrees C. and melting is rather complete atdegrees C., it is obvious that frictional contact between the saw bladeand the crystal, suflicient to produce a slight rise in temperature,will cause quite disastrous results and therefore must be kept at aminimum. An appreciable and very localized rise of temperature can thusbe easily caused which will result in cracking or breakage of thecrystal, primarily due to the large thermal expansion of the crystal.

It is therefore essential that any dust or crystalline matter whichadheres to the saw either as the result of the proximity of the saw tothe crystal being cut or on account of the loose material carried downby the saw being pressed against it either by the saw guides or theWheel over which the saw passes, be removed in order to prevent thethickness of the saw blade from building up to such an extent that itwill rub against the sides of the crystal in which the kerf is beingout.

One way of accomplishing this is to hold a hard metal tool, such as afile, .for example, against the side of the saw blade, but not incontact with the teeth, while the saw is running to scrape this materialfrom the saw blade and also to cause sulficient friction to raise thetemperature sufficiently to same as the guides and saw blade, in orderto avoid temperature inequalities tending to produce cracking .orwarping of the slabs during and after sawing. For if the crystal hasportions differing in temperature, then, after sawing, mechanicaldeformation may occur which can result in producing a slab in which thecut surface is not a plane, when the temperatures have equalized.

Reference should be had to the accompanying drawings forming a part ofthis specification in which:

Figure l is a side elevation of a band sawing machine.

Fig. 2 is a fragmentary section on line 2--2 in Fig. 1 showing the worktable.

Fig. 3 is an end elevation of the table and guides shown in Fig. 2.

Fig. 4 is a side elevation from the line 4-4 in Fig. 3.

In the drawings, the sawing machine has a suitable base frame 1 andcarries the wheels 2 and 3 over which the band saw 4 passes. The wheel 3is driven .from any suitable source of power, not shown, which drivesthe small wheel 5, shaft 6 and belt 7 which passes over pulleys 8 and 9.The upper portion of the sawing machine is provided with a standard 10to support the upper wheel 2 with its shaft 11 and extending from theframe 10 is a support arm 12 on which is mounted a suitable adjustableguide member 13, carrying fixed guide blocks 14 and adjust-able guideblocks 15 between which the band saw 4: passes.

A suitable support or table 16 is carried by the frame of the machine onwhich the crystal to be cut may be fed to the saw. On the table 16 ismounted a guide 17 to guide the crystal as it is fed toward the sawblade, and below the table 16 are mounted fixed guides 18 and adjustableguides 19, between which the band saw 4 passes.

In order to successfully saw such crystals rapidly and, with a minimumof breakage, I have found that it is necessary to use a saw with verysharp teeth and with the teeth set evenly with respect to the blade sothat i there are no teeth projecting considerably beyond the averageplane of the teeth. Also it is essential that the saw must be trued andheld so that it has substantially no play sidewise or in the plane ofthe blade. In order to prevent the sidewise play rigid guides 14, 15 and18, 19 may be secured above and below the table or support 16 on whichthe crystal is fed.to the saw and the saw blade must be trued upproperly to prevent movement in the plane of the blade. The teeth of thesaw must be so filed and set that the teeth are sharp and projectsubstantially uniformly beyond the planes of the blade of thesaw so thatthe sidesof the blade of the saw will not contact with the sides of thecrystal when a kerf is being cut.

Furthermore, I have found that it is necessary to run the saw at a speedwhich is a function of the extent or Width of the crystalline materialin contact with the saw teeth. In general, the greater the width ofcrystalline material, the slower the speed of the saw. This is toprevent undue localized heating of the crystalline material. I havefound, for example, in cutting a crystal in which the portion of thecrystal in contact With the teeth is approximately 2 that a relativelyslow speed, such as 500 lineal feet per minute is a desirable operatingspeed, whereas if the extent of material is very small, as in sawing asection from one of the slabs already out, then the speed may be verymaterially increased without any ill effects. In any event, the relationof the speed to the extent of surface cut must be such that thetemperature of the crystal in contact with the saw teeth must not exceed50 degrees C. over a relatively large area, and owing to the highcoelficient of thermal expansion a much smaller rise in a sharplylocalized area will produce disastrous cracklng.

It is also essential that the vibration of the band saw machine bereduced to a minimum. The crystal must fed substantially withoutvibration to the saw blade and further must not be subject to tooviolent shocks while resting on the table. In order that the crystal maybe fed'to the saw in a substantially straight line it is, of course,essential that a suitable guide 17 be provided against which the crystalis fed to the saw blade and it is desirable in order to obtain the bestresults that this guide have a width above the table at least as wide asthe width of the largest crystal to be sawed so that there is no dangerthat the crystal will not be fed toward the saw substantially in aplane. For the same reason this guide should extend on each side of thesaw a distance approximately equal to the length of the largest crystalto be sawed.

It is to be observed that, in general, the less heat there is generatedand allowed to remain in the crystal, the higher the cutting speed therecan be, and also that the type of saw may be varied so long as itsoperation conforms to the herein disclosed principles for the successfulcutting of sections of Rochelle salt crystals.

If desired, a suitable cooling or lubricating liquid may be used inconnection with the sawing of the crystal. However, if a cooling orlubricating liquid is used, it is preferable not to use such a liquidthat is ighly volatile, as this is liable toproduce cracks in thecrystal, due to the cooling ac-,'

tion of the volatile liquid, unless special preventative cautions aretaken.

To those skilled in the art many modifications of and widely differingembodiments and applications of my invention will suggest themselveswithout departing from the spirit and scope thereof. My disclosures andthe descriptions herein are purely illustrative and are not intended tobe in any sense limiting.

-lVhat I claim is:

1. The method of cutting sectionsfrom piezo-electric crystals of theRochellesalt type, which includes bringing the crystalline material to apredetermined temperature suitable for the material to be cut separatinga section from the crystal in substantially a single plane by removingthe crystalline particles continuously in the same direction at a rateof speed low enough to substantially prevent localized heating of thecrystalline material. i

2. The method of cutting sections from piezo-electric crystals oftheRochelle salt type, which includes bringing the crystalline materialto an o crating temperature, separating a section 0 the crystallinematerial from the crystal by removing continuously in the same directionsmall articles of crystalline material at a rate su ciently low toprevent a substantial localized rise of temperature of the crystallinematerial, and eliminating localized heating of any part of thecrystalline material by preventing the return of the particles removed.

3. The method of cutting sections from piezo-electric crystals, whichincludes bringing the crystal to a temperature suitable for cutting suchmaterial, cutting said material by continuously removing crystallinearticles from the crystal at a predetermmed speed which is inverselyproportional to the width of the material being cut, feeding the crystalin a straight line, and preventing engagement between the side walls ofthe kerf and the cutting means to avoid cracking of the crystal.

4:. The method of cutting sections from piezo-electric crystals, whichincludes bringing the crystal to a uniform cutting temperaturethroughout, cutting said material by continuously removing crystallineparticles from the crystal at a predetermined speed which is inverselyproportional to the width of the crystal being cut, feeding the crystalin a straight line, preventing engagement between the side walls of thekerf and the cutting means, and preventing the return of crystallineparticles to the crystal being cut.

5. The method of cutting sections from piezo-electric crystals of theRochelle salt type, which includes bringing the crystal to be cut tosubstantially the same temperature as the cutting means, continuouslyremoving crystalline particles from the crystal at a predetermined speedto separate the sections, continuously feeding the crystal, andpreventing engagement between the side walls of the kerf and the cuttingmeans to avoid cracking of the sections beingcut.

6. The method of cutting sections from.

piezo-electric crystals of the Rochelle salt type, which includesbringing the crystal to substantially the same temperature as thecutting means, separating the crystal by contlnuously cutting it in asingle plane, movmg the crystal in a plane substantially parallel to thecutting plane of the sections to be cut, and preventing the return ofagtially parallel to the plane of se aration ofthe sections, whereby asection 0 the crystal may be cut without undue heating and breakage ofthe crystal or section thereof.

8. The method of cutting sections from piezo-electric crystals of theRochelle salt type, which includes continuously removing crystallineparticles from the crystal in one direction and in substantially asingle plane, preventing the return of the removed particles of the kerfof the crystal being cut, and feeding the crystal in a plane parallel tothe plane of separation of the crystalline sections being cut.

9. The method of cutting sections from crystals of the Rochelle. salttype which consists in separating a section of the crystalline material.from the crystal by removing continuously in the same direction smallparticles of crystalline material at a rate sufficiently low to preventa substantial localized rise in temperature of the crystalline material,and eliminating localized heating of any part of the crystalline material by preventing the return of agglutinated crystal dust to the kerfbeing cut. 7

10. The method of cutting sections from crystals of the Rochellesalt'type, which consists in separating a section from the crystal bycontinuously cutting it in a single plane and in a single direction,moving the crystal in a plane substantially parallel to the cuttingplane of the section to be cut, and preventing the return ofagglutinated crystal dust to the section bein cutto avoid frictionalcontact between t e sides of the kerf being cut in the crystal and thebody portion of the vcutting means, thereby eliminating localizedheating of any part of the crystal.

11. The methodof cutting sections from crystals of the Rochelle salttype, which consists in cutting the material by removing crystallineparticles from the crystal at a rccletermined speed which is inverselyproportional to the width of the material being cut, preventingengagement between the side walls of the kerf and the body of thecutting means, and preventing the return of the removed crystallineparticles to the spaces between the side walls of the kerf and thecutting means to obviate cracking and localized heating of any part ofthe crystal and section being removed therefrom.

In testimony whereof I afiix my signature. v

' CHARLES B. SAWYER.

